The death toll from tornadoes and subsequent flooding late last week in Oklahoma has reached 20, the state medical examiner's office said, a day after the National Weather Service upgraded its rating of the twister that hit Oklahoma City to an EF5.

The Oklahoma medical examiner's office said Wednesday that the additional victim was a girl who died in Oklahoma City. Officials have said many of those who died in Oklahoma City were drowning victims who were swept away while taking shelter from the tornado in drainage ditches. Nine of the 20 victims died from blunt force injuries typical from flying debris in tornadoes.

On Tuesday, the National Weather Service said the Oklahoma City tornado – the second top-of-the-scale EF5 twister to hit the area in less than two weeks – had a record-breaking width of 2.6 miles (4 kilometers).

The weather service initially rated the tornado as an EF3, but it upgraded the ranking after surveying damage from the twister, which along with subsequent flooding killed 19 people, including three professional storm chasers. The weather service determined that the storm had winds reaching 295 mph (474 kph).

The Oklahoma City area has seen two of the extremely rare EF5 tornadoes in only 11 days. The other hit the suburb of Moore on May 20, killing 24 people and causing widespread damage. In 1999, Moore was hit by another EF5 with the strongest winds ever measured on Earth: 302 mph (486 kph).

William Hooke, a senior policy fellow with the American Meteorological Society, said the continued expansion of U. cities in the most tornado-prone areas makes it only a matter of time before one hits a heavily populated area.

"You dodged a bullet," Hooke said. "You lay that path over Oklahoma City, and you have devastation of biblical proportions.

"It's only a matter of time."

When the winds were at their most powerful Friday, no structures were nearby, said chief warning coordination meteorologist Rick Smith with the weather service.

"Any house would have been completely swept clean on the foundation. That's just my speculation," Smith said. "We're looking at extremes ... in the rare EF5 category. This in the super rare category because we don't deal with things like this often."

Smith said the storm's wide path would have made it hard to recognize up close.

"A two and a half mile wide tornado would not look like a tornado to a lot of people," Smith said.